Pitch retention member

ABSTRACT

A pitch retention member rotatably mounts a propeller or fan hereto radially outwardly from a spinner or a hub. The member attaches to the blade of a pair of tenons, each tenon having a hole passing therethrough for receiving a pin about which the blade may rotate. The pitch retention member cooperates with a motion limiter provided at the base of the blade to: damp rotational movement of the blade about the pin to minimize blade angular excursions when centrifugal loads are low; improve high speed blade stability; moderate blade vibratory motion and tune out undesirable blade resonant frequencies; and, absorb force created by impact with foreign objects. Such impact is adsorbed at a desired threshold level of bending load of a crushable material disposed within the blade retention pitch member.

CROSS REFERENCE TO RELATED APPLICATIONS

This invention described herein may employ some of the teachingsdisclosed and claimed in commonly owned copending applications filed oneven date herewith by Violette et al, (Ser. No. 07/255,815), entitled"Pinned Airfoil Propeller Assembly"; by Violette et al, (Ser. No.07/255,099), entitled "Pinned Airfoil Propeller Blade".

TECHNICAL FIELD

This invention relates to a pitch retention member for mounting apropeller blade to a hub.

BACKGROUND ART

Aircraft propeller blades are subject to damage from foreign objectssuch as sand, rain, hail, and birds etc. Propeller blades that aremounted towards the rear of an aircraft are particularly susceptible toforeign object damage. Runway debris, such as sand, runway markers,stones, ice, water, slush and segments of tire tread etc., may be kickedup into a plane of rotation of the blades. Collision between the foreignobjects and the propeller blades may require the removal of the damagedblades from the propeller for repair.

Typically, propeller blades are mounted to a hub of a propeller by meansof a pitch retention member. The member is rotatable within the hub toallow the pitch of the propeller blade mounted therein to be set asrequired. A spinner may enclose the hub and the member.

To replace a damaged blade, the spinner and/or the blade retentionmember and/or the hub may have to be disassembled. Because of thecomplexity of the disassembly (and subsequent reassembly), blade changesare time consuming, expensive and subject to error. The problem ismultiplied by propellers which have a plurality of blades. Somecounter-rotating prop-fan propellers may have as many as 18 blades.

In counter-rotation prop-fans, each blade is rather heavily loadedabsorbing as much as 1000 horsepower of engine torque and developing asmuch as 1,500 pounds of engine thrust. Heavily loaded propeller bladesare subject to high vibratory loads and stresses. Moreover becauseprop-fan blades are swept, they are subject to instability at highspeed.

DISCLOSURE OF THE INVENTION

It is an object of the invention to provide a pitch retention memberfrom which damaged propeller blades may be quickly and easily replaced.

It is a further object of the invention to increase the tolerance ofpropeller blades attached to the pitch retention member to foreignobject damage.

It is a further object of the invention to reduce blade vibratoryretention loads and stresses.

It is a further object of the invention to provide a pitch retentionmember that maximizes the stability of propeller blades mounted theretoand operating at higher speeds.

According to the invention, a pitch retention member has a propellerblade mounted thereto radially outwardly from a propeller spinner bymeans of a pin.

According to a feature of the invention, the pitch retention memberrotatably mounts the blades thereto by means of a pair of tenons, eachtenon having a hole passing therethrough for receiving the pin.

According to a further feature of the invention, the pitch retentionmember cooperates with a motion limiter provided at the base of theblade to damp rotational movement of the blade about the pin, tominimize blade angular excursions when centrifugal loads are low, tomoderate blade vibratory motion, to tune out undesirable blade resonatefrequencies, and to absorb force created by impact with foreign objects.Such impact is absorbed at a desired threshold level of bending load bymeans of a crushable material disposed within the blade retention pitchmember. By mounting the propeller blade for rotation about the axis ofthe pin, the blade response to a vibratory excitation in the first modeof vibration is modified such that the twisting motion of the blade isminimized. High speed stability of the blade is enhanced thereby.

These and other objects, features and advantages of the presentinvention will become more apparent in light of the following detaileddescription of a best mode embodiment thereof, as illustrated in theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a counter-rotating prop-fan propellerincorporating an embodiment of the invention;

FIG. 2 shows a perspective view, partially broken away, and partiallyexploded, of an embodiment of a propeller blade assembly of FIG. 1;

FIG. 3 shows a top view of a pitch retention member of FIG. 2; and

FIG. 4 shows a cut away view of the assembly of FIG. 2 taken along theline 4--4.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, a counter-rotating prop-fan propeller 10 whichprovides an environment for an embodiment of the invention is shown.Such a propeller 10 has a forward hub (not shown) covered by a firstspinner 12, and an aft hub (not shown) covered by a second spinner 14.Each hub, as is known in the art, holds a pitch retention member 16 (seeFIGS. 2 and 3). Each pitch retention member, in turn, has a blade 18mounted thereto. Each blade may be rotated angularly about itslongitudinal axis 20 by the blade pitch retention member to set thepitch of the blade as is well known in the art.

Referring to FIGS. 2 and 4, a best mode embodiment of the propellerblade of the invention is shown. The propeller blade is utilized in anassembly which has several major portions; the blade pitch retentionmember (hereinafter member) 16, the blade 18, and a retention pin 22.

THE BLADE

The blade 18 is comprised of: a spar formed of an insert 24, wrappingmaterial 30 (see FIG. 4) and a spar root fairing 40 having an integralrotation limiter 42; a first filler material 26, a second fillermaterial 28 (see FIG. 4), an airfoil shell having a first side 32 and asecond side 34, a leading edge sheath 36, and a pin access panel 38. Theblade has a root portion 44, a leading edge 46, a trailing edge 48 and atip portion 50 as is well known in the art.

The insert 24 is constructed of a graphite epoxy, Kevlar®, or fiberglasscomposite material (or the like) and is shaped to approximate theinternal geometry of both sides of the shell 32, 34 which, in turn, formfinal shape of the blade 18. The first filler material 26, which is alightweight structural foam, provides structural integrity and shearstrength to the leading and trail edge portions which overhang the spar.The second filler material 28, which is a pre-molded elastomericmaterial, is used to shape the root 40 as will be discussed infra. Thespar wrapping material 30 is constructed of a preimpregnated graphitetape, cloth or the like. The first side 32 and the second side 34 of theshell are constructed of fiberglass cloth or the like, filled withtransfer molded resins as are known in the art. The leading edge sheath36, which is constructed of an electroformed nickel, protects theleading edge 46 of the blade from erosion and foreign object damage.

The pin access panel 38, which is located at the root portion 44 andtrailing edge 48 of the blade 18, is shaped generally to conform withthe shape of the root edge and trailing edge thereof. The pin accesspanel has two aerodynamic side portions 52, a bottom portion 54, and atrailing portion 56.

The pin access panel has two or more holes 58 passing therethrough toallow pin access panel to be secured to the first side 32 of the shell.The pin access panel has an inner contour 60 which cooperates with anouter contour 62 of the first side 32 and second side 34 of the shell toensure an aerodynamic profile of the blade 18. The holes 58 align withan equal number of threaded holes 64 (or bushings or the like) disposedwithin the first side 32 of the shell. Screws 66 secure the pin accesspanel to the shell.

The spar root fairing 40 is comprised of a body 68 having a hollow core70, a pair of mortise sections 72 extending into the body, a pair ofside portions 74 which extend upwardly from the body, a cavity 76 formedbetween the side portions for receiving the insert 24 (see FIG. 4), andthe rotation limiter 42 extending downwardly from the body. A bushing 73is disposed within the length of the hollow core 70. The side portions74 taper in width and in length upwardly from the body so that the sideportions fair into the spar when the cavity receives the insert 24 (seeFIGS. 2 and 4).

The rotation limiter 42 tapers in width downwardly from the body portion(see FIG. 4) and then extends outwardly to form a bulbous portion 78.The bulbous portion helps retain the rotation limiter within the member16 as will be discussed infra.

The blade 18 is of common spar and shell construction. The spar,comprised of the insert 24, the wrapping material 30, and the rootfairing 40, forms the primary structure of the blade. The first side 32and the second side 34 of the shell extend beyond the boundaries of thespar to form the external airfoil. Cavities formed between the first andsecond sides of the shell ar filled with the first filler material 26.

The spar is formed by first bonding the insert 24 to the spar rootfairing 40 by means of an adhesive as is known in the art. The spar androot fairing are then used as a mandrel to wrap the wrapping material 30therearound.

The second filler material 28 is appended to the wrapping material 30 bymeans of a silicon type adhesive. The second filler sections give theblade a profile at its root which prevents air from escaping between theroot portion 44 of the blade and the spinner 12. The second fillershapes the root portion of the blade so that it fairs to the spinner 12or 14 and so that it provides an aerodynamic shape in conjunction withthe member 16, as will be discussed infra.

The spar and the first side 32 and second side 34 of the shell arebonded to each other along their mutual interface by means of anadhesive film. The insert is bonded to the spar root fairing by means ofa similar adhesive film.

THE MEMBER

The member 16 is conventionally mounted within the hub for rotation toset the pitch of the blades as is well known in the art.

The member has a pair of tenons 80 for insertion in the mortise sections72 of the spar root fairing 40. The sides of the tenons cooperate withthe second filler material and the wraps of the root portion of theblade to form an efficient aerodynamic shape. The tenons each have anopening 110 in which a bushing 108 is mounted.

The member has an opening 82 in its center as seen in FIG. 3. Theopening has four lobes 84, 86, 88, 90. A liner 91, which conforms to theshape of the opening, is slideably received within the lobes thereof.Each of a pair of first elastomeric members 92 is bonded conventionallyto the liner 91 within one of an opposing first pair of lobes 86, 90.

Each elastomeric member is in turn conventionally bonded to an oblong,first metallic (or other deformable material) member 94. Bonded withineach end 96 of the first metallic member is a second elastomeric member98. As shown in FIG. 4, each second elastomeric member 98 has an arcuatecross-section 100. The arcuate cross-sections abut the bulbous end 78 ofthe rotation limiter 42.

A second metallic (or other deformable material) member 104 is attachedto the liner 91 across each of lobes 84, 88. Bonded to the secondmetallic member and the liner 91 is a crushable material 106 such as ahoneycomb. An air space 102 separates the first and second metallicmembers. The liner is slideably removable from its respective lobe forrepair and replacement. The member may be enclosed by a removable cover103 (shown in phantom in FIG. 4) which fairs into the spinner 12 or 14to provide an aerodynamic profile at the root portion 44.

THE RETENTION PIN

The retention pin 22 is formed of a hollow cylinder. The diameter of thecylinder conforms to the inner diameter of the bushings 73, 108. Theretention pin has an threaded interior portion (not shown). The threadedinterior portion is designed to engage a threaded key (not shown) bywhich the pin may be withdrawn from the hollow core 70 of the fairing 40and the openings 110 within the tenons 80.

ASSEMBLY

To construct the assembly, the rotation limiter 42 of the fairing 40 isinserted between the second elastomeric members 98 as the tenons 80 ofthe member 16 are inserted in mortise sections 72 of the fairing 40.When the holes 110 in the tenons align with the hollow core 70, theretention pin 22 is inserted therethrough. The holes 58 of the pinaccess panel 38 are aligned with the holes 64 in the first side of theshell. The pin access panel is then attached to the first side of theshell by screws 66.

If a blade is damaged and requires maintenance, the screws 66 holdingthe pin access panel 38 are removed so that access to the pin 22 ispossible. The threads of the key (not shown) engage the pin. The pin isthen removed by pulling the key. The blade may then be easily removedand replaced as above.

If a blade experiences impact from a foreign object, the impulsiveenergy of the impact will cause rotation of the blade about the pin. Theimpulsive energy is distributed through the rotation limiter across thesecond elastomeric members 98 in compression, across the firstelastomeric members 92 in shear, and across the first and secondmetallic members to the crushable material. The crushable material isdesigned to crush if a threshold bending moment that would damage theblade is distributed across the air space 102 thereto. That is, thecrushable material is designed to absorb a force of rotational motionexceeding a threshold bending moment limit upon the propeller or fanblade. On the other hand, the first and second elastomeric members andthe first and second metallic members will resist the force ofrotational motion below the threshold bending moment limit. Because thecrushable material absorbs the force of the bending moment, theprobability of damage to the blade is minimized. The second metallicmember ensures that the force of the bending moment is evenlydistributed across the crushable material. The liner makes it easier toslideably remove the crushable material mounted therein from itsrespective lobe.

In contrast to blades that may not rotate about a retention pin,rotation of the blade of the invention about the retention pin preventsthe building of bending loads in the root portion of the compositeportions of the spar thereby minimizing the probability of the fractureof relatively brittle composite portions. Blades that do notredistribute the bending moment caused by impacts must have rootportions that are sized to withstand such bending moments. Such rootportions become inordinately thick and are inefficient aerodynamically.Such inefficiency is particularly inappropriate in the prop fanenvironment where tip speeds of propeller blades may exceed Mach 1 andwhere flow between the blade root sections is accelerated due to achoking effect to speeds approaching Mach 1.

The composite insert and wraps provide several benefits. The finishedblade is light weight. As a result, the pin 22 is able to reliablywithstand the centrifugal loads placed thereon. A pin may not be able towithstand the loads of heavier blades. Also, the blades are strongenough to provide extended service and durability. Further, putting thepin in the blade allows the spar wrap material to overhang forward andaft of the retention tenons, thereby increasing the load capacity of theassembly.

The first and second elastomeric members resist the tendency of theblade to rotate about the pin in shear and compression as noted above.The durometer hardness and dimensions of the elastomeric used in theelastomeric members may be designed to tune out undesirable bladeresonate frequencies, to reduce stress on the blade, and to minimizeblade angular excursions when centrifugal loads are low.

The first mode of vibration in straight blades is characterized by apure bending motion. Because of an overhanging tip mass, the first modeof vibration in swept blades is characterized by both a twisting motionand a bending motion. The twisting motion acts to magnify blade responseto vibratory excitations produced by the distortions of the aerodynamicflow field through the propeller thereby leading to high speedinstabilities. By mounting the propeller blade for rotation about theaxis of the pin, the blade response to the vibratory excitation in thefirst mode of vibration is modified such that the twisting motion of theblade is minimized. The first mode of vibration in the swept blade ofthe invention is characterized by a more pure bending motion than anequivalent fixed root blade. High speed stability is enhanced thereby.Blades that twist torsionally require stiffening to withstand suchtorsional twist. By utilizing the pin assembly, thinner and shorterchord length blades, which are quieter and more efficientaerodynamically than the prior art, may be utilized. Further thestability of the swept blade is maximized with the blade beingessentially free of flutter at blade tips speeds of about Mach 1.

Although the invention has been shown and described with respect to abest mode embodiment thereof, it should be understood by those skilledin the art that the foregoing and various other changes, omissions, andadditions in the form and detail thereof maybe made therein withoutdeparting from the spirit and scope of the invention. For instance oneof ordinary skill in the art would recognize the applicability of theinvention to fan blades as well as propeller blades.

We claim:
 1. A pitch member for rotatably mounting a propeller or fanblade to a hub, said propeller or fan blade having means dependingtherefrom for limiting rotation of said propeller or fan or fan bladeabout a root portion thereof, said member comprising;a opening forreceiving said means for limiting rotation, first means disposed withinsaid opening for resisting a force of rotational motion of saidpropeller or fan blade about said root portion thereof below a thresholdbending moment limit upon said propeller or fan blade, and second meansdisposed within said opening for absorbing said force of rotationalmotion of said propeller or fan blade about said root portion thereofexceeding a threshold bending moment limit upon said propeller or fanblade.
 2. The pitch member of claim 1 further comprising;a linerremovably disposed within said opening and attaching to said first meansand said second means such that said first and second means may beremoved within said liner as required.
 3. The pitch member of claim 1wherein said opening comprises;a first and second pair of lobes, saidfirst pair of lobes receiving said first means, said second pair oflobes housing said second means.
 4. The pitch member of claim 3 whereinsaid first means comprises;a first elastomeric member disposed withinone of said first pair of lobes, said first member resisting said forceof rotation of said propeller or fan blade in shear, a first memberattaching to said first elastomeric member, and a second elastomericmember disposed within said first member, said second elastomeric memberresisting said force of rotation of said propeller or fan blade incompression.
 5. The pitch member of claim 4 wherein said second meanscompromises;a crushable means having a crushable material disposedwithin said second pair of lobes, said crushable means abutting saidfirst member.
 6. The pitch member of claim 1 wherein said first meanscomprises;a first elastomeric member disposed within said opening, saidfirst member resisting said force of rotation of said propeller or fanblade in shear, a first member attaching to said first elastomericmember, and a second elastomeric member disposed within said firstmember, said second elastomeric member resisting said force of rotationof said propeller or fan blade in compression.
 7. The pitch member ofclaim 6 wherein said second means compromises;a crushable means having acrushable material disposed within said opening, said crushable meansabutting said first member.
 8. The pitch member of claim 1 wherein saidsecond means compromises;a crushable means having a crushable materialdisposed within said opening for absorbing said force of rotationalmotion of said propeller or fan blade about said root portion thereofexceeding a threshold bending moment limit upon said propeller or fanblade.
 9. The pitch member of claim 8 wherein said first meanscomprises;a first elastomeric member disposed within said opening, saidfirst member resisting said force of rotation of said propeller or fanblade in shear, a first member attaching to said first elastomericmember and abutting said crushable means, said first member transmittingsaid rotational force of said propeller or fan blade to said crushablematerial, and a second elastomeric member disposed within said firstmember, said second elastomeric member resisting said force of rotationof said propeller or fan blade in compression.
 10. A pitch member formounting a propeller or fan or fan blade to a hub to set a pitch of saidpropeller or fan blade, said propeller or fan blade having meansdepending therefrom for limiting rotation of said propeller or fan bladeabout a root portion thereof, said member comprising;a body, a openingwithin said body for receiving said means for limiting rotation, firstmeans disposed within said opening for resisting a force of rotationalmotion of said propeller or fan blade about said root portion thereofbelow a threshold bending moment limit upon said propeller or fan blade,second means disposed within said opening for absorbing said force ofrotational motion of said propeller or fan blade about said root portionthereof exceeding a threshold bending moment limit upon said propelleror fan blade, and means extending from said body for rotatably mountingsaid propeller or fan blade radially outwardly from said hub.
 11. Thepitch member of claim 10 further comprising;a liner removably disposedwithin said opening and attaching to said first means and said secondmeans such that said first and second means may be removed with saidliner as required.
 12. The pitch member of claim 10 wherein said meansextending from said body is characterized by a tenon.
 13. The pitchmember of claim 12 wherein said tenon is characterized by a hole passingtherethrough for rotatably locking said blade to said tenon.
 14. Thepitch member of claim 13 wherein said opening comprises;a first andsecond pair of lobes, said first pair of lobes receiving said firstmeans, said second pair of lobes housing said second means.
 15. Thepitch member of claim 14 wherein said first means comprises;a firstelastomeric member disposed within one of said first pair of lobes, saidfirst member resisting said force of rotation of said propeller or fanblade in shear, a first member attaching to said first elastomericmember, and a second elastomeric member disposed within said member,said second elastomeric member resisting first member, said secondelastomeric member resisting said force of rotation of said propeller orfan blade in compression.
 16. The pitch member of claim 15 wherein saidsecond means compromises;a crushable means having a crushable materialdisposed within said second pair of lobes, said crushable means abuttingsaid first member.
 17. The pitch member of claim 10 wherein said firstmeans comprises;a first elastomeric member disposed within said opening,said first member resisting said force of rotation of said propeller orfan blade in shear, a first member attaching to said first elastomericmember, and a second elastomeric member disposed within said firstmember, said second elastomeric member resisting said force of rotationof said propeller or fan blade in compression.
 18. The pitch member ofclaim 17 wherein said second means compromises;a crushable means havinga crushable material disposed within said opening, said crushable meansabutting said first member.
 19. The pitch member of claim 10 whereinsaid second means compromises;a crushable means having a crushablematerial disposed within said opening for absorbing said force ofrotational motion of said propeller or fan blade exceeding said rootportion thereof above a threshold bending moment limit upon saidpropeller or fan blade.
 20. The pitch member of claim 19 wherein saidfirst means comprises;a first elastomeric member disposed within saidopening, said first member resisting said force of rotation of saidpropeller or fan blade in shear, a first member attaching to said firstelastomeric member and abutting said crushable means, said first membertransmitting said rotational force of said propeller or fan blade tosaid crushable material, and a second elastomeric member disposed withinsaid first member, said second elastomeric member resisting said forceof rotation of said propeller or fan blade in compression.